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  <div class="section" id="transports-and-protocols">
<span id="asyncio-transports-protocols"></span><h1>Transports and Protocols<a class="headerlink" href="#transports-and-protocols" title="Permalink to this headline">¶</a></h1>
<p class="rubric">Preface</p>
<p>Transports and Protocols are used by the <strong>low-level</strong> event loop
APIs such as <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_connection" title="asyncio.loop.create_connection"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_connection()</span></code></a>.  They use
callback-based programming style and enable high-performance
implementations of network or IPC protocols (e.g. HTTP).</p>
<p>Essentially, transports and protocols should only be used in
libraries and frameworks and never in high-level asyncio
applications.</p>
<p>This documentation page covers both <a class="reference internal" href="#transports">Transports</a> and <a class="reference internal" href="#protocols">Protocols</a>.</p>
<p class="rubric">Introduction</p>
<p>At the highest level, the transport is concerned with <em>how</em> bytes
are transmitted, while the protocol determines <em>which</em> bytes to
transmit (and to some extent when).</p>
<p>A different way of saying the same thing: a transport is an
abstraction for a socket (or similar I/O endpoint) while a protocol
is an abstraction for an application, from the transport’s point
of view.</p>
<p>Yet another view is the transport and protocol interfaces
together define an abstract interface for using network I/O and
interprocess I/O.</p>
<p>There is always a 1:1 relationship between transport and protocol
objects: the protocol calls transport methods to send data,
while the transport calls protocol methods to pass it data that
has been received.</p>
<p>Most of connection oriented event loop methods
(such as <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_connection" title="asyncio.loop.create_connection"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_connection()</span></code></a>) usually accept a
<em>protocol_factory</em> argument used to create a <em>Protocol</em> object
for an accepted connection, represented by a <em>Transport</em> object.
Such methods usually return a tuple of <code class="docutils literal notranslate"><span class="pre">(transport,</span> <span class="pre">protocol)</span></code>.</p>
<p class="rubric">Contents</p>
<p>This documentation page contains the following sections:</p>
<ul class="simple">
<li>The <a class="reference internal" href="#transports">Transports</a> section documents asyncio <a class="reference internal" href="#asyncio.BaseTransport" title="asyncio.BaseTransport"><code class="xref py py-class docutils literal notranslate"><span class="pre">BaseTransport</span></code></a>,
<a class="reference internal" href="#asyncio.ReadTransport" title="asyncio.ReadTransport"><code class="xref py py-class docutils literal notranslate"><span class="pre">ReadTransport</span></code></a>, <a class="reference internal" href="#asyncio.WriteTransport" title="asyncio.WriteTransport"><code class="xref py py-class docutils literal notranslate"><span class="pre">WriteTransport</span></code></a>, <a class="reference internal" href="#asyncio.Transport" title="asyncio.Transport"><code class="xref py py-class docutils literal notranslate"><span class="pre">Transport</span></code></a>,
<a class="reference internal" href="#asyncio.DatagramTransport" title="asyncio.DatagramTransport"><code class="xref py py-class docutils literal notranslate"><span class="pre">DatagramTransport</span></code></a>, and <a class="reference internal" href="#asyncio.SubprocessTransport" title="asyncio.SubprocessTransport"><code class="xref py py-class docutils literal notranslate"><span class="pre">SubprocessTransport</span></code></a>
classes.</li>
<li>The <a class="reference internal" href="#protocols">Protocols</a> section documents asyncio <a class="reference internal" href="#asyncio.BaseProtocol" title="asyncio.BaseProtocol"><code class="xref py py-class docutils literal notranslate"><span class="pre">BaseProtocol</span></code></a>,
<a class="reference internal" href="#asyncio.Protocol" title="asyncio.Protocol"><code class="xref py py-class docutils literal notranslate"><span class="pre">Protocol</span></code></a>, <a class="reference internal" href="#asyncio.BufferedProtocol" title="asyncio.BufferedProtocol"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedProtocol</span></code></a>,
<a class="reference internal" href="#asyncio.DatagramProtocol" title="asyncio.DatagramProtocol"><code class="xref py py-class docutils literal notranslate"><span class="pre">DatagramProtocol</span></code></a>, and <a class="reference internal" href="#asyncio.SubprocessProtocol" title="asyncio.SubprocessProtocol"><code class="xref py py-class docutils literal notranslate"><span class="pre">SubprocessProtocol</span></code></a> classes.</li>
<li>The <a class="reference internal" href="#examples">Examples</a> section showcases how to work with transports,
protocols, and low-level event loop APIs.</li>
</ul>
<div class="section" id="transports">
<span id="asyncio-transport"></span><h2>Transports<a class="headerlink" href="#transports" title="Permalink to this headline">¶</a></h2>
<p>Transports are classes provided by <a class="reference internal" href="asyncio.html#module-asyncio" title="asyncio: Asynchronous I/O."><code class="xref py py-mod docutils literal notranslate"><span class="pre">asyncio</span></code></a> in order to abstract
various kinds of communication channels.</p>
<p>Transport objects are always instantiated by an
ref:<cite>asyncio event loop &lt;asyncio-event-loop&gt;</cite>.</p>
<p>asyncio implements transports for TCP, UDP, SSL, and subprocess pipes.
The methods available on a transport depend on the transport’s kind.</p>
<p>The transport classes are <a class="reference internal" href="asyncio-dev.html#asyncio-multithreading"><span class="std std-ref">not thread safe</span></a>.</p>
<div class="section" id="transports-hierarchy">
<h3>Transports Hierarchy<a class="headerlink" href="#transports-hierarchy" title="Permalink to this headline">¶</a></h3>
<dl class="class">
<dt id="asyncio.BaseTransport">
<em class="property">class </em><code class="descclassname">asyncio.</code><code class="descname">BaseTransport</code><a class="headerlink" href="#asyncio.BaseTransport" title="Permalink to this definition">¶</a></dt>
<dd><p>Base class for all transports.  Contains methods that all
asyncio transports share.</p>
</dd></dl>

<dl class="class">
<dt id="asyncio.WriteTransport">
<em class="property">class </em><code class="descclassname">asyncio.</code><code class="descname">WriteTransport</code><span class="sig-paren">(</span><em>BaseTransport</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.WriteTransport" title="Permalink to this definition">¶</a></dt>
<dd><p>A base transport for write-only connections.</p>
<p>Instances of the <em>WriteTransport</em> class are returned from
the <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.connect_write_pipe" title="asyncio.loop.connect_write_pipe"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.connect_write_pipe()</span></code></a> event loop method and
are also used by subprocess-related methods like
<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.subprocess_exec" title="asyncio.loop.subprocess_exec"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.subprocess_exec()</span></code></a>.</p>
</dd></dl>

<dl class="class">
<dt id="asyncio.ReadTransport">
<em class="property">class </em><code class="descclassname">asyncio.</code><code class="descname">ReadTransport</code><span class="sig-paren">(</span><em>BaseTransport</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.ReadTransport" title="Permalink to this definition">¶</a></dt>
<dd><p>A base transport for read-only connections.</p>
<p>Instances of the <em>ReadTransport</em> class are returned from
the <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.connect_read_pipe" title="asyncio.loop.connect_read_pipe"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.connect_read_pipe()</span></code></a> event loop method and
are also used by subprocess-related methods like
<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.subprocess_exec" title="asyncio.loop.subprocess_exec"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.subprocess_exec()</span></code></a>.</p>
</dd></dl>

<dl class="class">
<dt id="asyncio.Transport">
<em class="property">class </em><code class="descclassname">asyncio.</code><code class="descname">Transport</code><span class="sig-paren">(</span><em>WriteTransport</em>, <em>ReadTransport</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Transport" title="Permalink to this definition">¶</a></dt>
<dd><p>Interface representing a bidirectional transport, such as a
TCP connection.</p>
<p>The user does not instantiate a transport directly; they call a
utility function, passing it a protocol factory and other
information necessary to create the transport and protocol.</p>
<p>Instances of the <em>Transport</em> class are returned from or used by
event loop methods like <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_connection" title="asyncio.loop.create_connection"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_connection()</span></code></a>,
<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_unix_connection" title="asyncio.loop.create_unix_connection"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_unix_connection()</span></code></a>,
<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_server" title="asyncio.loop.create_server"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_server()</span></code></a>, <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.sendfile" title="asyncio.loop.sendfile"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.sendfile()</span></code></a>, etc.</p>
</dd></dl>

<dl class="class">
<dt id="asyncio.DatagramTransport">
<em class="property">class </em><code class="descclassname">asyncio.</code><code class="descname">DatagramTransport</code><span class="sig-paren">(</span><em>BaseTransport</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.DatagramTransport" title="Permalink to this definition">¶</a></dt>
<dd><p>A transport for datagram (UDP) connections.</p>
<p>Instances of the <em>DatagramTransport</em> class are returned from
the <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_datagram_endpoint" title="asyncio.loop.create_datagram_endpoint"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_datagram_endpoint()</span></code></a> event loop method.</p>
</dd></dl>

<dl class="class">
<dt id="asyncio.SubprocessTransport">
<em class="property">class </em><code class="descclassname">asyncio.</code><code class="descname">SubprocessTransport</code><span class="sig-paren">(</span><em>BaseTransport</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.SubprocessTransport" title="Permalink to this definition">¶</a></dt>
<dd><p>An abstraction to represent a connection between a parent and its
child OS process.</p>
<p>Instances of the <em>SubprocessTransport</em> class are returned from
event loop methods <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.subprocess_shell" title="asyncio.loop.subprocess_shell"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.subprocess_shell()</span></code></a> and
<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.subprocess_exec" title="asyncio.loop.subprocess_exec"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.subprocess_exec()</span></code></a>.</p>
</dd></dl>

</div>
<div class="section" id="base-transport">
<h3>Base Transport<a class="headerlink" href="#base-transport" title="Permalink to this headline">¶</a></h3>
<dl class="method">
<dt id="asyncio.BaseTransport.close">
<code class="descclassname">BaseTransport.</code><code class="descname">close</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseTransport.close" title="Permalink to this definition">¶</a></dt>
<dd><p>Close the transport.</p>
<p>If the transport has a buffer for outgoing
data, buffered data will be flushed asynchronously.  No more data
will be received.  After all buffered data is flushed, the
protocol’s <a class="reference internal" href="#asyncio.BaseProtocol.connection_lost" title="asyncio.BaseProtocol.connection_lost"><code class="xref py py-meth docutils literal notranslate"><span class="pre">protocol.connection_lost()</span></code></a> method will be called with
<a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a> as its argument.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.BaseTransport.is_closing">
<code class="descclassname">BaseTransport.</code><code class="descname">is_closing</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseTransport.is_closing" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the transport is closing or is closed.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.BaseTransport.get_extra_info">
<code class="descclassname">BaseTransport.</code><code class="descname">get_extra_info</code><span class="sig-paren">(</span><em>name</em>, <em>default=None</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseTransport.get_extra_info" title="Permalink to this definition">¶</a></dt>
<dd><p>Return information about the transport or underlying resources
it uses.</p>
<p><em>name</em> is a string representing the piece of transport-specific
information to get.</p>
<p><em>default</em> is the value to return if the information is not
available, or if the transport does not support querying it
with the given third-party event loop implementation or on the
current platform.</p>
<p>For example, the following code attempts to get the underlying
socket object of the transport:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">sock</span> <span class="o">=</span> <span class="n">transport</span><span class="o">.</span><span class="n">get_extra_info</span><span class="p">(</span><span class="s1">&#39;socket&#39;</span><span class="p">)</span>
<span class="k">if</span> <span class="n">sock</span> <span class="ow">is</span> <span class="ow">not</span> <span class="kc">None</span><span class="p">:</span>
    <span class="nb">print</span><span class="p">(</span><span class="n">sock</span><span class="o">.</span><span class="n">getsockopt</span><span class="p">(</span><span class="o">...</span><span class="p">))</span>
</pre></div>
</div>
<p>Categories of information that can be queried on some transports:</p>
<ul class="simple">
<li>socket:<ul>
<li><code class="docutils literal notranslate"><span class="pre">'peername'</span></code>: the remote address to which the socket is
connected, result of <a class="reference internal" href="socket.html#socket.socket.getpeername" title="socket.socket.getpeername"><code class="xref py py-meth docutils literal notranslate"><span class="pre">socket.socket.getpeername()</span></code></a>
(<code class="docutils literal notranslate"><span class="pre">None</span></code> on error)</li>
<li><code class="docutils literal notranslate"><span class="pre">'socket'</span></code>: <a class="reference internal" href="socket.html#socket.socket" title="socket.socket"><code class="xref py py-class docutils literal notranslate"><span class="pre">socket.socket</span></code></a> instance</li>
<li><code class="docutils literal notranslate"><span class="pre">'sockname'</span></code>: the socket’s own address,
result of <a class="reference internal" href="socket.html#socket.socket.getsockname" title="socket.socket.getsockname"><code class="xref py py-meth docutils literal notranslate"><span class="pre">socket.socket.getsockname()</span></code></a></li>
</ul>
</li>
<li>SSL socket:<ul>
<li><code class="docutils literal notranslate"><span class="pre">'compression'</span></code>: the compression algorithm being used as a
string, or <code class="docutils literal notranslate"><span class="pre">None</span></code> if the connection isn’t compressed; result
of <a class="reference internal" href="ssl.html#ssl.SSLSocket.compression" title="ssl.SSLSocket.compression"><code class="xref py py-meth docutils literal notranslate"><span class="pre">ssl.SSLSocket.compression()</span></code></a></li>
<li><code class="docutils literal notranslate"><span class="pre">'cipher'</span></code>: a three-value tuple containing the name of the
cipher being used, the version of the SSL protocol that defines
its use, and the number of secret bits being used; result of
<a class="reference internal" href="ssl.html#ssl.SSLSocket.cipher" title="ssl.SSLSocket.cipher"><code class="xref py py-meth docutils literal notranslate"><span class="pre">ssl.SSLSocket.cipher()</span></code></a></li>
<li><code class="docutils literal notranslate"><span class="pre">'peercert'</span></code>: peer certificate; result of
<a class="reference internal" href="ssl.html#ssl.SSLSocket.getpeercert" title="ssl.SSLSocket.getpeercert"><code class="xref py py-meth docutils literal notranslate"><span class="pre">ssl.SSLSocket.getpeercert()</span></code></a></li>
<li><code class="docutils literal notranslate"><span class="pre">'sslcontext'</span></code>: <a class="reference internal" href="ssl.html#ssl.SSLContext" title="ssl.SSLContext"><code class="xref py py-class docutils literal notranslate"><span class="pre">ssl.SSLContext</span></code></a> instance</li>
<li><code class="docutils literal notranslate"><span class="pre">'ssl_object'</span></code>: <a class="reference internal" href="ssl.html#ssl.SSLObject" title="ssl.SSLObject"><code class="xref py py-class docutils literal notranslate"><span class="pre">ssl.SSLObject</span></code></a> or
<a class="reference internal" href="ssl.html#ssl.SSLSocket" title="ssl.SSLSocket"><code class="xref py py-class docutils literal notranslate"><span class="pre">ssl.SSLSocket</span></code></a> instance</li>
</ul>
</li>
<li>pipe:<ul>
<li><code class="docutils literal notranslate"><span class="pre">'pipe'</span></code>: pipe object</li>
</ul>
</li>
<li>subprocess:<ul>
<li><code class="docutils literal notranslate"><span class="pre">'subprocess'</span></code>: <a class="reference internal" href="subprocess.html#subprocess.Popen" title="subprocess.Popen"><code class="xref py py-class docutils literal notranslate"><span class="pre">subprocess.Popen</span></code></a> instance</li>
</ul>
</li>
</ul>
</dd></dl>

<dl class="method">
<dt id="asyncio.BaseTransport.set_protocol">
<code class="descclassname">BaseTransport.</code><code class="descname">set_protocol</code><span class="sig-paren">(</span><em>protocol</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseTransport.set_protocol" title="Permalink to this definition">¶</a></dt>
<dd><p>Set a new protocol.</p>
<p>Switching protocol should only be done when both
protocols are documented to support the switch.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.BaseTransport.get_protocol">
<code class="descclassname">BaseTransport.</code><code class="descname">get_protocol</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseTransport.get_protocol" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the current protocol.</p>
</dd></dl>

</div>
<div class="section" id="read-only-transports">
<h3>Read-only Transports<a class="headerlink" href="#read-only-transports" title="Permalink to this headline">¶</a></h3>
<dl class="method">
<dt id="asyncio.ReadTransport.is_reading">
<code class="descclassname">ReadTransport.</code><code class="descname">is_reading</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.ReadTransport.is_reading" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the transport is receiving new data.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.7.</span></p>
</div>
</dd></dl>

<dl class="method">
<dt id="asyncio.ReadTransport.pause_reading">
<code class="descclassname">ReadTransport.</code><code class="descname">pause_reading</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.ReadTransport.pause_reading" title="Permalink to this definition">¶</a></dt>
<dd><p>Pause the receiving end of the transport.  No data will be passed to
the protocol’s <a class="reference internal" href="#asyncio.Protocol.data_received" title="asyncio.Protocol.data_received"><code class="xref py py-meth docutils literal notranslate"><span class="pre">protocol.data_received()</span></code></a>
method until <a class="reference internal" href="#asyncio.ReadTransport.resume_reading" title="asyncio.ReadTransport.resume_reading"><code class="xref py py-meth docutils literal notranslate"><span class="pre">resume_reading()</span></code></a> is called.</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.7: </span>The method is idempotent, i.e. it can be called when the
transport is already paused or closed.</p>
</div>
</dd></dl>

<dl class="method">
<dt id="asyncio.ReadTransport.resume_reading">
<code class="descclassname">ReadTransport.</code><code class="descname">resume_reading</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.ReadTransport.resume_reading" title="Permalink to this definition">¶</a></dt>
<dd><p>Resume the receiving end.  The protocol’s
<a class="reference internal" href="#asyncio.Protocol.data_received" title="asyncio.Protocol.data_received"><code class="xref py py-meth docutils literal notranslate"><span class="pre">protocol.data_received()</span></code></a> method
will be called once again if some data is available for reading.</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.7: </span>The method is idempotent, i.e. it can be called when the
transport is already reading.</p>
</div>
</dd></dl>

</div>
<div class="section" id="write-only-transports">
<h3>Write-only Transports<a class="headerlink" href="#write-only-transports" title="Permalink to this headline">¶</a></h3>
<dl class="method">
<dt id="asyncio.WriteTransport.abort">
<code class="descclassname">WriteTransport.</code><code class="descname">abort</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.WriteTransport.abort" title="Permalink to this definition">¶</a></dt>
<dd><p>Close the transport immediately, without waiting for pending operations
to complete.  Buffered data will be lost.  No more data will be received.
The protocol’s <a class="reference internal" href="#asyncio.BaseProtocol.connection_lost" title="asyncio.BaseProtocol.connection_lost"><code class="xref py py-meth docutils literal notranslate"><span class="pre">protocol.connection_lost()</span></code></a> method will eventually be
called with <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a> as its argument.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.WriteTransport.can_write_eof">
<code class="descclassname">WriteTransport.</code><code class="descname">can_write_eof</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.WriteTransport.can_write_eof" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-const docutils literal notranslate"><span class="pre">True</span></code></a> if the transport supports
<a class="reference internal" href="#asyncio.WriteTransport.write_eof" title="asyncio.WriteTransport.write_eof"><code class="xref py py-meth docutils literal notranslate"><span class="pre">write_eof()</span></code></a>, <a class="reference internal" href="constants.html#False" title="False"><code class="xref py py-const docutils literal notranslate"><span class="pre">False</span></code></a> if not.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.WriteTransport.get_write_buffer_size">
<code class="descclassname">WriteTransport.</code><code class="descname">get_write_buffer_size</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.WriteTransport.get_write_buffer_size" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the current size of the output buffer used by the transport.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.WriteTransport.get_write_buffer_limits">
<code class="descclassname">WriteTransport.</code><code class="descname">get_write_buffer_limits</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.WriteTransport.get_write_buffer_limits" title="Permalink to this definition">¶</a></dt>
<dd><p>Get the <em>high</em> and <em>low</em> watermarks for write flow control. Return a
tuple <code class="docutils literal notranslate"><span class="pre">(low,</span> <span class="pre">high)</span></code> where <em>low</em> and <em>high</em> are positive number of
bytes.</p>
<p>Use <a class="reference internal" href="#asyncio.WriteTransport.set_write_buffer_limits" title="asyncio.WriteTransport.set_write_buffer_limits"><code class="xref py py-meth docutils literal notranslate"><span class="pre">set_write_buffer_limits()</span></code></a> to set the limits.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.4.2.</span></p>
</div>
</dd></dl>

<dl class="method">
<dt id="asyncio.WriteTransport.set_write_buffer_limits">
<code class="descclassname">WriteTransport.</code><code class="descname">set_write_buffer_limits</code><span class="sig-paren">(</span><em>high=None</em>, <em>low=None</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.WriteTransport.set_write_buffer_limits" title="Permalink to this definition">¶</a></dt>
<dd><p>Set the <em>high</em> and <em>low</em> watermarks for write flow control.</p>
<p>These two values (measured in number of
bytes) control when the protocol’s
<a class="reference internal" href="#asyncio.BaseProtocol.pause_writing" title="asyncio.BaseProtocol.pause_writing"><code class="xref py py-meth docutils literal notranslate"><span class="pre">protocol.pause_writing()</span></code></a>
and <a class="reference internal" href="#asyncio.BaseProtocol.resume_writing" title="asyncio.BaseProtocol.resume_writing"><code class="xref py py-meth docutils literal notranslate"><span class="pre">protocol.resume_writing()</span></code></a>
methods are called. If specified, the low watermark must be less
than or equal to the high watermark.  Neither <em>high</em> nor <em>low</em>
can be negative.</p>
<p><a class="reference internal" href="#asyncio.BaseProtocol.pause_writing" title="asyncio.BaseProtocol.pause_writing"><code class="xref py py-meth docutils literal notranslate"><span class="pre">pause_writing()</span></code></a> is called when the buffer size
becomes greater than or equal to the <em>high</em> value. If writing has
been paused, <a class="reference internal" href="#asyncio.BaseProtocol.resume_writing" title="asyncio.BaseProtocol.resume_writing"><code class="xref py py-meth docutils literal notranslate"><span class="pre">resume_writing()</span></code></a> is called when
the buffer size becomes less than or equal to the <em>low</em> value.</p>
<p>The defaults are implementation-specific.  If only the
high watermark is given, the low watermark defaults to an
implementation-specific value less than or equal to the
high watermark.  Setting <em>high</em> to zero forces <em>low</em> to zero as
well, and causes <a class="reference internal" href="#asyncio.BaseProtocol.pause_writing" title="asyncio.BaseProtocol.pause_writing"><code class="xref py py-meth docutils literal notranslate"><span class="pre">pause_writing()</span></code></a> to be called
whenever the buffer becomes non-empty.  Setting <em>low</em> to zero causes
<a class="reference internal" href="#asyncio.BaseProtocol.resume_writing" title="asyncio.BaseProtocol.resume_writing"><code class="xref py py-meth docutils literal notranslate"><span class="pre">resume_writing()</span></code></a> to be called only once the
buffer is empty. Use of zero for either limit is generally
sub-optimal as it reduces opportunities for doing I/O and
computation concurrently.</p>
<p>Use <a class="reference internal" href="#asyncio.WriteTransport.get_write_buffer_limits" title="asyncio.WriteTransport.get_write_buffer_limits"><code class="xref py py-meth docutils literal notranslate"><span class="pre">get_write_buffer_limits()</span></code></a>
to get the limits.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.WriteTransport.write">
<code class="descclassname">WriteTransport.</code><code class="descname">write</code><span class="sig-paren">(</span><em>data</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.WriteTransport.write" title="Permalink to this definition">¶</a></dt>
<dd><p>Write some <em>data</em> bytes to the transport.</p>
<p>This method does not block; it buffers the data and arranges for it
to be sent out asynchronously.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.WriteTransport.writelines">
<code class="descclassname">WriteTransport.</code><code class="descname">writelines</code><span class="sig-paren">(</span><em>list_of_data</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.WriteTransport.writelines" title="Permalink to this definition">¶</a></dt>
<dd><p>Write a list (or any iterable) of data bytes to the transport.
This is functionally equivalent to calling <a class="reference internal" href="#asyncio.WriteTransport.write" title="asyncio.WriteTransport.write"><code class="xref py py-meth docutils literal notranslate"><span class="pre">write()</span></code></a> on each
element yielded by the iterable, but may be implemented more
efficiently.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.WriteTransport.write_eof">
<code class="descclassname">WriteTransport.</code><code class="descname">write_eof</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.WriteTransport.write_eof" title="Permalink to this definition">¶</a></dt>
<dd><p>Close the write end of the transport after flushing all buffered data.
Data may still be received.</p>
<p>This method can raise <a class="reference internal" href="exceptions.html#NotImplementedError" title="NotImplementedError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">NotImplementedError</span></code></a> if the transport
(e.g. SSL) doesn’t support half-closed connections.</p>
</dd></dl>

</div>
<div class="section" id="datagram-transports">
<h3>Datagram Transports<a class="headerlink" href="#datagram-transports" title="Permalink to this headline">¶</a></h3>
<dl class="method">
<dt id="asyncio.DatagramTransport.sendto">
<code class="descclassname">DatagramTransport.</code><code class="descname">sendto</code><span class="sig-paren">(</span><em>data</em>, <em>addr=None</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.DatagramTransport.sendto" title="Permalink to this definition">¶</a></dt>
<dd><p>Send the <em>data</em> bytes to the remote peer given by <em>addr</em> (a
transport-dependent target address).  If <em>addr</em> is <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a>,
the data is sent to the target address given on transport
creation.</p>
<p>This method does not block; it buffers the data and arranges
for it to be sent out asynchronously.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.DatagramTransport.abort">
<code class="descclassname">DatagramTransport.</code><code class="descname">abort</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.DatagramTransport.abort" title="Permalink to this definition">¶</a></dt>
<dd><p>Close the transport immediately, without waiting for pending
operations to complete.  Buffered data will be lost.
No more data will be received.  The protocol’s
<a class="reference internal" href="#asyncio.BaseProtocol.connection_lost" title="asyncio.BaseProtocol.connection_lost"><code class="xref py py-meth docutils literal notranslate"><span class="pre">protocol.connection_lost()</span></code></a>
method will eventually be called with <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a> as its argument.</p>
</dd></dl>

</div>
<div class="section" id="subprocess-transports">
<span id="asyncio-subprocess-transports"></span><h3>Subprocess Transports<a class="headerlink" href="#subprocess-transports" title="Permalink to this headline">¶</a></h3>
<dl class="method">
<dt id="asyncio.SubprocessTransport.get_pid">
<code class="descclassname">SubprocessTransport.</code><code class="descname">get_pid</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.SubprocessTransport.get_pid" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the subprocess process id as an integer.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.SubprocessTransport.get_pipe_transport">
<code class="descclassname">SubprocessTransport.</code><code class="descname">get_pipe_transport</code><span class="sig-paren">(</span><em>fd</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.SubprocessTransport.get_pipe_transport" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the transport for the communication pipe corresponding to the
integer file descriptor <em>fd</em>:</p>
<ul class="simple">
<li><code class="docutils literal notranslate"><span class="pre">0</span></code>: readable streaming transport of the standard input (<em>stdin</em>),
or <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a> if the subprocess was not created with <code class="docutils literal notranslate"><span class="pre">stdin=PIPE</span></code></li>
<li><code class="docutils literal notranslate"><span class="pre">1</span></code>: writable streaming transport of the standard output (<em>stdout</em>),
or <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a> if the subprocess was not created with <code class="docutils literal notranslate"><span class="pre">stdout=PIPE</span></code></li>
<li><code class="docutils literal notranslate"><span class="pre">2</span></code>: writable streaming transport of the standard error (<em>stderr</em>),
or <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a> if the subprocess was not created with <code class="docutils literal notranslate"><span class="pre">stderr=PIPE</span></code></li>
<li>other <em>fd</em>: <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a></li>
</ul>
</dd></dl>

<dl class="method">
<dt id="asyncio.SubprocessTransport.get_returncode">
<code class="descclassname">SubprocessTransport.</code><code class="descname">get_returncode</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.SubprocessTransport.get_returncode" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the subprocess return code as an integer or <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a>
if it hasn’t returned, which is similar to the
<a class="reference internal" href="subprocess.html#subprocess.Popen.returncode" title="subprocess.Popen.returncode"><code class="xref py py-attr docutils literal notranslate"><span class="pre">subprocess.Popen.returncode</span></code></a> attribute.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.SubprocessTransport.kill">
<code class="descclassname">SubprocessTransport.</code><code class="descname">kill</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.SubprocessTransport.kill" title="Permalink to this definition">¶</a></dt>
<dd><p>Kill the subprocess.</p>
<p>On POSIX systems, the function sends SIGKILL to the subprocess.
On Windows, this method is an alias for <a class="reference internal" href="#asyncio.SubprocessTransport.terminate" title="asyncio.SubprocessTransport.terminate"><code class="xref py py-meth docutils literal notranslate"><span class="pre">terminate()</span></code></a>.</p>
<p>See also <a class="reference internal" href="subprocess.html#subprocess.Popen.kill" title="subprocess.Popen.kill"><code class="xref py py-meth docutils literal notranslate"><span class="pre">subprocess.Popen.kill()</span></code></a>.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.SubprocessTransport.send_signal">
<code class="descclassname">SubprocessTransport.</code><code class="descname">send_signal</code><span class="sig-paren">(</span><em>signal</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.SubprocessTransport.send_signal" title="Permalink to this definition">¶</a></dt>
<dd><p>Send the <em>signal</em> number to the subprocess, as in
<a class="reference internal" href="subprocess.html#subprocess.Popen.send_signal" title="subprocess.Popen.send_signal"><code class="xref py py-meth docutils literal notranslate"><span class="pre">subprocess.Popen.send_signal()</span></code></a>.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.SubprocessTransport.terminate">
<code class="descclassname">SubprocessTransport.</code><code class="descname">terminate</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.SubprocessTransport.terminate" title="Permalink to this definition">¶</a></dt>
<dd><p>Stop the subprocess.</p>
<p>On POSIX systems, this method sends SIGTERM to the subprocess.
On Windows, the Windows API function TerminateProcess() is called to
stop the subprocess.</p>
<p>See also <a class="reference internal" href="subprocess.html#subprocess.Popen.terminate" title="subprocess.Popen.terminate"><code class="xref py py-meth docutils literal notranslate"><span class="pre">subprocess.Popen.terminate()</span></code></a>.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.SubprocessTransport.close">
<code class="descclassname">SubprocessTransport.</code><code class="descname">close</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.SubprocessTransport.close" title="Permalink to this definition">¶</a></dt>
<dd><p>Kill the subprocess by calling the <a class="reference internal" href="#asyncio.SubprocessTransport.kill" title="asyncio.SubprocessTransport.kill"><code class="xref py py-meth docutils literal notranslate"><span class="pre">kill()</span></code></a> method.</p>
<p>If the subprocess hasn’t returned yet, and close transports of
<em>stdin</em>, <em>stdout</em>, and <em>stderr</em> pipes.</p>
</dd></dl>

</div>
</div>
<div class="section" id="protocols">
<span id="asyncio-protocol"></span><h2>Protocols<a class="headerlink" href="#protocols" title="Permalink to this headline">¶</a></h2>
<p>asyncio provides a set of abstract base classes that should be used
to implement network protocols.  Those classes are meant to be used
together with <a class="reference internal" href="#asyncio-transport"><span class="std std-ref">transports</span></a>.</p>
<p>Subclasses of abstract base protocol classes may implement some or
all methods.  All these methods are callbacks: they are called by
transports on certain events, for example when some data is received.
A base protocol method should be called by the corresponding transport.</p>
<div class="section" id="base-protocols">
<h3>Base Protocols<a class="headerlink" href="#base-protocols" title="Permalink to this headline">¶</a></h3>
<dl class="class">
<dt id="asyncio.BaseProtocol">
<em class="property">class </em><code class="descclassname">asyncio.</code><code class="descname">BaseProtocol</code><a class="headerlink" href="#asyncio.BaseProtocol" title="Permalink to this definition">¶</a></dt>
<dd><p>Base protocol with methods that all protocols share.</p>
</dd></dl>

<dl class="class">
<dt id="asyncio.Protocol">
<em class="property">class </em><code class="descclassname">asyncio.</code><code class="descname">Protocol</code><span class="sig-paren">(</span><em>BaseProtocol</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Protocol" title="Permalink to this definition">¶</a></dt>
<dd><p>The base class for implementing streaming protocols
(TCP, Unix sockets, etc).</p>
</dd></dl>

<dl class="class">
<dt id="asyncio.BufferedProtocol">
<em class="property">class </em><code class="descclassname">asyncio.</code><code class="descname">BufferedProtocol</code><span class="sig-paren">(</span><em>BaseProtocol</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BufferedProtocol" title="Permalink to this definition">¶</a></dt>
<dd><p>A base class for implementing streaming protocols with manual
control of the receive buffer.</p>
</dd></dl>

<dl class="class">
<dt id="asyncio.DatagramProtocol">
<em class="property">class </em><code class="descclassname">asyncio.</code><code class="descname">DatagramProtocol</code><span class="sig-paren">(</span><em>BaseProtocol</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.DatagramProtocol" title="Permalink to this definition">¶</a></dt>
<dd><p>The base class for implementing datagram (UDP) protocols.</p>
</dd></dl>

<dl class="class">
<dt id="asyncio.SubprocessProtocol">
<em class="property">class </em><code class="descclassname">asyncio.</code><code class="descname">SubprocessProtocol</code><span class="sig-paren">(</span><em>BaseProtocol</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.SubprocessProtocol" title="Permalink to this definition">¶</a></dt>
<dd><p>The base class for implementing protocols communicating with child
processes (unidirectional pipes).</p>
</dd></dl>

</div>
<div class="section" id="base-protocol">
<h3>Base Protocol<a class="headerlink" href="#base-protocol" title="Permalink to this headline">¶</a></h3>
<p>All asyncio protocols can implement Base Protocol callbacks.</p>
<p class="rubric">Connection Callbacks</p>
<p>Connection callbacks are called on all protocols, exactly once per
a successful connection.  All other protocol callbacks can only be
called between those two methods.</p>
<dl class="method">
<dt id="asyncio.BaseProtocol.connection_made">
<code class="descclassname">BaseProtocol.</code><code class="descname">connection_made</code><span class="sig-paren">(</span><em>transport</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseProtocol.connection_made" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when a connection is made.</p>
<p>The <em>transport</em> argument is the transport representing the
connection.  The protocol is responsible for storing the reference
to its transport.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.BaseProtocol.connection_lost">
<code class="descclassname">BaseProtocol.</code><code class="descname">connection_lost</code><span class="sig-paren">(</span><em>exc</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseProtocol.connection_lost" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when the connection is lost or closed.</p>
<p>The argument is either an exception object or <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-const docutils literal notranslate"><span class="pre">None</span></code></a>.
The latter means a regular EOF is received, or the connection was
aborted or closed by this side of the connection.</p>
</dd></dl>

<p class="rubric">Flow Control Callbacks</p>
<p>Flow control callbacks can be called by transports to pause or
resume writing performed by the protocol.</p>
<p>See the documentation of the <a class="reference internal" href="#asyncio.WriteTransport.set_write_buffer_limits" title="asyncio.WriteTransport.set_write_buffer_limits"><code class="xref py py-meth docutils literal notranslate"><span class="pre">set_write_buffer_limits()</span></code></a>
method for more details.</p>
<dl class="method">
<dt id="asyncio.BaseProtocol.pause_writing">
<code class="descclassname">BaseProtocol.</code><code class="descname">pause_writing</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseProtocol.pause_writing" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when the transport’s buffer goes over the high watermark.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.BaseProtocol.resume_writing">
<code class="descclassname">BaseProtocol.</code><code class="descname">resume_writing</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BaseProtocol.resume_writing" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when the transport’s buffer drains below the low watermark.</p>
</dd></dl>

<p>If the buffer size equals the high watermark,
<a class="reference internal" href="#asyncio.BaseProtocol.pause_writing" title="asyncio.BaseProtocol.pause_writing"><code class="xref py py-meth docutils literal notranslate"><span class="pre">pause_writing()</span></code></a> is not called: the buffer size must
go strictly over.</p>
<p>Conversely, <a class="reference internal" href="#asyncio.BaseProtocol.resume_writing" title="asyncio.BaseProtocol.resume_writing"><code class="xref py py-meth docutils literal notranslate"><span class="pre">resume_writing()</span></code></a> is called when the
buffer size is equal or lower than the low watermark.  These end
conditions are important to ensure that things go as expected when
either mark is zero.</p>
</div>
<div class="section" id="streaming-protocols">
<h3>Streaming Protocols<a class="headerlink" href="#streaming-protocols" title="Permalink to this headline">¶</a></h3>
<p>Event methods, such as <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_server" title="asyncio.loop.create_server"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_server()</span></code></a>,
<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_unix_server" title="asyncio.loop.create_unix_server"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_unix_server()</span></code></a>, <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_connection" title="asyncio.loop.create_connection"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_connection()</span></code></a>,
<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_unix_connection" title="asyncio.loop.create_unix_connection"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_unix_connection()</span></code></a>, <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.connect_accepted_socket" title="asyncio.loop.connect_accepted_socket"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.connect_accepted_socket()</span></code></a>,
<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.connect_read_pipe" title="asyncio.loop.connect_read_pipe"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.connect_read_pipe()</span></code></a>, and <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.connect_write_pipe" title="asyncio.loop.connect_write_pipe"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.connect_write_pipe()</span></code></a>
accept factories that return streaming protocols.</p>
<dl class="method">
<dt id="asyncio.Protocol.data_received">
<code class="descclassname">Protocol.</code><code class="descname">data_received</code><span class="sig-paren">(</span><em>data</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Protocol.data_received" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when some data is received.  <em>data</em> is a non-empty bytes
object containing the incoming data.</p>
<p>Whether the data is buffered, chunked or reassembled depends on
the transport.  In general, you shouldn’t rely on specific semantics
and instead make your parsing generic and flexible. However,
data is always received in the correct order.</p>
<p>The method can be called an arbitrary number of times while
a connection is open.</p>
<p>However, <a class="reference internal" href="#asyncio.Protocol.eof_received" title="asyncio.Protocol.eof_received"><code class="xref py py-meth docutils literal notranslate"><span class="pre">protocol.eof_received()</span></code></a>
is called at most once.  Once <cite>eof_received()</cite> is called,
<code class="docutils literal notranslate"><span class="pre">data_received()</span></code> is not called anymore.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.Protocol.eof_received">
<code class="descclassname">Protocol.</code><code class="descname">eof_received</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Protocol.eof_received" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when the other end signals it won’t send any more data
(for example by calling <a class="reference internal" href="#asyncio.WriteTransport.write_eof" title="asyncio.WriteTransport.write_eof"><code class="xref py py-meth docutils literal notranslate"><span class="pre">transport.write_eof()</span></code></a>, if the other end also uses
asyncio).</p>
<p>This method may return a false value (including <code class="docutils literal notranslate"><span class="pre">None</span></code>), in which case
the transport will close itself.  Conversely, if this method returns a
true value, the protocol used determines whether to close the transport.
Since the default implementation returns <code class="docutils literal notranslate"><span class="pre">None</span></code>, it implicitly closes the
connection.</p>
<p>Some transports, including SSL, don’t support half-closed connections,
in which case returning true from this method will result in the connection
being closed.</p>
</dd></dl>

<p>State machine:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>start -&gt; connection_made
    [-&gt; data_received]*
    [-&gt; eof_received]?
-&gt; connection_lost -&gt; end
</pre></div>
</div>
</div>
<div class="section" id="buffered-streaming-protocols">
<h3>Buffered Streaming Protocols<a class="headerlink" href="#buffered-streaming-protocols" title="Permalink to this headline">¶</a></h3>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.7: </span><strong>Important:</strong> this has been added to asyncio in Python 3.7
<em>on a provisional basis</em>!  This is as an experimental API that
might be changed or removed completely in Python 3.8.</p>
</div>
<p>Buffered Protocols can be used with any event loop method
that supports <a class="reference internal" href="#streaming-protocols">Streaming Protocols</a>.</p>
<p><code class="docutils literal notranslate"><span class="pre">BufferedProtocol</span></code> implementations allow explicit manual allocation
and control of the receive buffer.  Event loops can then use the buffer
provided by the protocol to avoid unnecessary data copies.  This
can result in noticeable performance improvement for protocols that
receive big amounts of data.  Sophisticated protocol implementations
can significantly reduce the number of buffer allocations.</p>
<p>The following callbacks are called on <a class="reference internal" href="#asyncio.BufferedProtocol" title="asyncio.BufferedProtocol"><code class="xref py py-class docutils literal notranslate"><span class="pre">BufferedProtocol</span></code></a>
instances:</p>
<dl class="method">
<dt id="asyncio.BufferedProtocol.get_buffer">
<code class="descclassname">BufferedProtocol.</code><code class="descname">get_buffer</code><span class="sig-paren">(</span><em>sizehint</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BufferedProtocol.get_buffer" title="Permalink to this definition">¶</a></dt>
<dd><p>Called to allocate a new receive buffer.</p>
<p><em>sizehint</em> is the recommended minimum size for the returned
buffer.  It is acceptable to return smaller or larger buffers
than what <em>sizehint</em> suggests.  When set to -1, the buffer size
can be arbitrary. It is an error to return a buffer with a zero size.</p>
<p><code class="docutils literal notranslate"><span class="pre">get_buffer()</span></code> must return an object implementing the
<a class="reference internal" href="../c-api/buffer.html#bufferobjects"><span class="std std-ref">buffer protocol</span></a>.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.BufferedProtocol.buffer_updated">
<code class="descclassname">BufferedProtocol.</code><code class="descname">buffer_updated</code><span class="sig-paren">(</span><em>nbytes</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BufferedProtocol.buffer_updated" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when the buffer was updated with the received data.</p>
<p><em>nbytes</em> is the total number of bytes that were written to the buffer.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.BufferedProtocol.eof_received">
<code class="descclassname">BufferedProtocol.</code><code class="descname">eof_received</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.BufferedProtocol.eof_received" title="Permalink to this definition">¶</a></dt>
<dd><p>See the documentation of the <a class="reference internal" href="#asyncio.Protocol.eof_received" title="asyncio.Protocol.eof_received"><code class="xref py py-meth docutils literal notranslate"><span class="pre">protocol.eof_received()</span></code></a> method.</p>
</dd></dl>

<p><a class="reference internal" href="#asyncio.BufferedProtocol.get_buffer" title="asyncio.BufferedProtocol.get_buffer"><code class="xref py py-meth docutils literal notranslate"><span class="pre">get_buffer()</span></code></a> can be called an arbitrary number
of times during a connection.  However, <a class="reference internal" href="#asyncio.Protocol.eof_received" title="asyncio.Protocol.eof_received"><code class="xref py py-meth docutils literal notranslate"><span class="pre">protocol.eof_received()</span></code></a> is called at most once
and, if called, <a class="reference internal" href="#asyncio.BufferedProtocol.get_buffer" title="asyncio.BufferedProtocol.get_buffer"><code class="xref py py-meth docutils literal notranslate"><span class="pre">get_buffer()</span></code></a> and
<a class="reference internal" href="#asyncio.BufferedProtocol.buffer_updated" title="asyncio.BufferedProtocol.buffer_updated"><code class="xref py py-meth docutils literal notranslate"><span class="pre">buffer_updated()</span></code></a> won’t be called after it.</p>
<p>State machine:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>start -&gt; connection_made
    [-&gt; get_buffer
        [-&gt; buffer_updated]?
    ]*
    [-&gt; eof_received]?
-&gt; connection_lost -&gt; end
</pre></div>
</div>
</div>
<div class="section" id="datagram-protocols">
<h3>Datagram Protocols<a class="headerlink" href="#datagram-protocols" title="Permalink to this headline">¶</a></h3>
<p>Datagram Protocol instances should be constructed by protocol
factories passed to the <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_datagram_endpoint" title="asyncio.loop.create_datagram_endpoint"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_datagram_endpoint()</span></code></a> method.</p>
<dl class="method">
<dt id="asyncio.DatagramProtocol.datagram_received">
<code class="descclassname">DatagramProtocol.</code><code class="descname">datagram_received</code><span class="sig-paren">(</span><em>data</em>, <em>addr</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.DatagramProtocol.datagram_received" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when a datagram is received.  <em>data</em> is a bytes object containing
the incoming data.  <em>addr</em> is the address of the peer sending the data;
the exact format depends on the transport.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.DatagramProtocol.error_received">
<code class="descclassname">DatagramProtocol.</code><code class="descname">error_received</code><span class="sig-paren">(</span><em>exc</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.DatagramProtocol.error_received" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when a previous send or receive operation raises an
<a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-class docutils literal notranslate"><span class="pre">OSError</span></code></a>.  <em>exc</em> is the <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-class docutils literal notranslate"><span class="pre">OSError</span></code></a> instance.</p>
<p>This method is called in rare conditions, when the transport (e.g. UDP)
detects that a datagram could not be delivered to its recipient.
In many conditions though, undeliverable datagrams will be silently
dropped.</p>
</dd></dl>

<div class="admonition note">
<p class="first admonition-title">Note</p>
<p>On BSD systems (macOS, FreeBSD, etc.) flow control is not supported
for datagram protocols, because there is no reliable way to detect send
failures caused by writing too many packets.</p>
<p class="last">The socket always appears ‘ready’ and excess packets are dropped. An
<a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-class docutils literal notranslate"><span class="pre">OSError</span></code></a> with <code class="docutils literal notranslate"><span class="pre">errno</span></code> set to <a class="reference internal" href="errno.html#errno.ENOBUFS" title="errno.ENOBUFS"><code class="xref py py-const docutils literal notranslate"><span class="pre">errno.ENOBUFS</span></code></a> may
or may not be raised; if it is raised, it will be reported to
<a class="reference internal" href="#asyncio.DatagramProtocol.error_received" title="asyncio.DatagramProtocol.error_received"><code class="xref py py-meth docutils literal notranslate"><span class="pre">DatagramProtocol.error_received()</span></code></a> but otherwise ignored.</p>
</div>
</div>
<div class="section" id="subprocess-protocols">
<span id="asyncio-subprocess-protocols"></span><h3>Subprocess Protocols<a class="headerlink" href="#subprocess-protocols" title="Permalink to this headline">¶</a></h3>
<p>Datagram Protocol instances should be constructed by protocol
factories passed to the <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.subprocess_exec" title="asyncio.loop.subprocess_exec"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.subprocess_exec()</span></code></a> and
<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.subprocess_shell" title="asyncio.loop.subprocess_shell"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.subprocess_shell()</span></code></a> methods.</p>
<dl class="method">
<dt id="asyncio.SubprocessProtocol.pipe_data_received">
<code class="descclassname">SubprocessProtocol.</code><code class="descname">pipe_data_received</code><span class="sig-paren">(</span><em>fd</em>, <em>data</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.SubprocessProtocol.pipe_data_received" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when the child process writes data into its stdout or stderr
pipe.</p>
<p><em>fd</em> is the integer file descriptor of the pipe.</p>
<p><em>data</em> is a non-empty bytes object containing the received data.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.SubprocessProtocol.pipe_connection_lost">
<code class="descclassname">SubprocessProtocol.</code><code class="descname">pipe_connection_lost</code><span class="sig-paren">(</span><em>fd</em>, <em>exc</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.SubprocessProtocol.pipe_connection_lost" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when one of the pipes communicating with the child process
is closed.</p>
<p><em>fd</em> is the integer file descriptor that was closed.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.SubprocessProtocol.process_exited">
<code class="descclassname">SubprocessProtocol.</code><code class="descname">process_exited</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.SubprocessProtocol.process_exited" title="Permalink to this definition">¶</a></dt>
<dd><p>Called when the child process has exited.</p>
</dd></dl>

</div>
</div>
<div class="section" id="examples">
<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
<div class="section" id="tcp-echo-server">
<span id="asyncio-example-tcp-echo-server-protocol"></span><h3>TCP Echo Server<a class="headerlink" href="#tcp-echo-server" title="Permalink to this headline">¶</a></h3>
<p>Create a TCP echo server using the <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_server" title="asyncio.loop.create_server"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_server()</span></code></a> method, send back
received data, and close the connection:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>


<span class="k">class</span> <span class="nc">EchoServerProtocol</span><span class="p">(</span><span class="n">asyncio</span><span class="o">.</span><span class="n">Protocol</span><span class="p">):</span>
    <span class="k">def</span> <span class="nf">connection_made</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">transport</span><span class="p">):</span>
        <span class="n">peername</span> <span class="o">=</span> <span class="n">transport</span><span class="o">.</span><span class="n">get_extra_info</span><span class="p">(</span><span class="s1">&#39;peername&#39;</span><span class="p">)</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Connection from </span><span class="si">{}</span><span class="s1">&#39;</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">peername</span><span class="p">))</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span> <span class="o">=</span> <span class="n">transport</span>

    <span class="k">def</span> <span class="nf">data_received</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">data</span><span class="p">):</span>
        <span class="n">message</span> <span class="o">=</span> <span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">()</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Data received: </span><span class="si">{!r}</span><span class="s1">&#39;</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">message</span><span class="p">))</span>

        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Send: </span><span class="si">{!r}</span><span class="s1">&#39;</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">message</span><span class="p">))</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>

        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Close the client socket&#39;</span><span class="p">)</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>


<span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
    <span class="c1"># Get a reference to the event loop as we plan to use</span>
    <span class="c1"># low-level APIs.</span>
    <span class="n">loop</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">get_running_loop</span><span class="p">()</span>

    <span class="n">server</span> <span class="o">=</span> <span class="k">await</span> <span class="n">loop</span><span class="o">.</span><span class="n">create_server</span><span class="p">(</span>
        <span class="k">lambda</span><span class="p">:</span> <span class="n">EchoServerProtocol</span><span class="p">(),</span>
        <span class="s1">&#39;127.0.0.1&#39;</span><span class="p">,</span> <span class="mi">8888</span><span class="p">)</span>

    <span class="k">async</span> <span class="k">with</span> <span class="n">server</span><span class="p">:</span>
        <span class="k">await</span> <span class="n">server</span><span class="o">.</span><span class="n">serve_forever</span><span class="p">()</span>


<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>
</pre></div>
</div>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last">The <a class="reference internal" href="asyncio-stream.html#asyncio-tcp-echo-server-streams"><span class="std std-ref">TCP echo server using streams</span></a>
example uses the high-level <a class="reference internal" href="asyncio-stream.html#asyncio.start_server" title="asyncio.start_server"><code class="xref py py-func docutils literal notranslate"><span class="pre">asyncio.start_server()</span></code></a> function.</p>
</div>
</div>
<div class="section" id="tcp-echo-client">
<span id="asyncio-example-tcp-echo-client-protocol"></span><h3>TCP Echo Client<a class="headerlink" href="#tcp-echo-client" title="Permalink to this headline">¶</a></h3>
<p>A TCP echo client using the <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_connection" title="asyncio.loop.create_connection"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_connection()</span></code></a> method, sends
data, and waits until the connection is closed:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>


<span class="k">class</span> <span class="nc">EchoClientProtocol</span><span class="p">(</span><span class="n">asyncio</span><span class="o">.</span><span class="n">Protocol</span><span class="p">):</span>
    <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">message</span><span class="p">,</span> <span class="n">on_con_lost</span><span class="p">,</span> <span class="n">loop</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">message</span> <span class="o">=</span> <span class="n">message</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">loop</span> <span class="o">=</span> <span class="n">loop</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">on_con_lost</span> <span class="o">=</span> <span class="n">on_con_lost</span>

    <span class="k">def</span> <span class="nf">connection_made</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">transport</span><span class="p">):</span>
        <span class="n">transport</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">message</span><span class="o">.</span><span class="n">encode</span><span class="p">())</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Data sent: </span><span class="si">{!r}</span><span class="s1">&#39;</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">message</span><span class="p">))</span>

    <span class="k">def</span> <span class="nf">data_received</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">data</span><span class="p">):</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Data received: </span><span class="si">{!r}</span><span class="s1">&#39;</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">()))</span>

    <span class="k">def</span> <span class="nf">connection_lost</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">exc</span><span class="p">):</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;The server closed the connection&#39;</span><span class="p">)</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">on_con_lost</span><span class="o">.</span><span class="n">set_result</span><span class="p">(</span><span class="kc">True</span><span class="p">)</span>


<span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
    <span class="c1"># Get a reference to the event loop as we plan to use</span>
    <span class="c1"># low-level APIs.</span>
    <span class="n">loop</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">get_running_loop</span><span class="p">()</span>

    <span class="n">on_con_lost</span> <span class="o">=</span> <span class="n">loop</span><span class="o">.</span><span class="n">create_future</span><span class="p">()</span>
    <span class="n">message</span> <span class="o">=</span> <span class="s1">&#39;Hello World!&#39;</span>

    <span class="n">transport</span><span class="p">,</span> <span class="n">protocol</span> <span class="o">=</span> <span class="k">await</span> <span class="n">loop</span><span class="o">.</span><span class="n">create_connection</span><span class="p">(</span>
        <span class="k">lambda</span><span class="p">:</span> <span class="n">EchoClientProtocol</span><span class="p">(</span><span class="n">message</span><span class="p">,</span> <span class="n">on_con_lost</span><span class="p">,</span> <span class="n">loop</span><span class="p">),</span>
        <span class="s1">&#39;127.0.0.1&#39;</span><span class="p">,</span> <span class="mi">8888</span><span class="p">)</span>

    <span class="c1"># Wait until the protocol signals that the connection</span>
    <span class="c1"># is lost and close the transport.</span>
    <span class="k">try</span><span class="p">:</span>
        <span class="k">await</span> <span class="n">on_con_lost</span>
    <span class="k">finally</span><span class="p">:</span>
        <span class="n">transport</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>


<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>
</pre></div>
</div>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last">The <a class="reference internal" href="asyncio-stream.html#asyncio-tcp-echo-client-streams"><span class="std std-ref">TCP echo client using streams</span></a>
example uses the high-level <a class="reference internal" href="asyncio-stream.html#asyncio.open_connection" title="asyncio.open_connection"><code class="xref py py-func docutils literal notranslate"><span class="pre">asyncio.open_connection()</span></code></a> function.</p>
</div>
</div>
<div class="section" id="udp-echo-server">
<span id="asyncio-udp-echo-server-protocol"></span><h3>UDP Echo Server<a class="headerlink" href="#udp-echo-server" title="Permalink to this headline">¶</a></h3>
<p>A UDP echo server, using the <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_datagram_endpoint" title="asyncio.loop.create_datagram_endpoint"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_datagram_endpoint()</span></code></a>
method, sends back received data:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>


<span class="k">class</span> <span class="nc">EchoServerProtocol</span><span class="p">:</span>
    <span class="k">def</span> <span class="nf">connection_made</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">transport</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span> <span class="o">=</span> <span class="n">transport</span>

    <span class="k">def</span> <span class="nf">datagram_received</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">data</span><span class="p">,</span> <span class="n">addr</span><span class="p">):</span>
        <span class="n">message</span> <span class="o">=</span> <span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">()</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Received </span><span class="si">%r</span><span class="s1"> from </span><span class="si">%s</span><span class="s1">&#39;</span> <span class="o">%</span> <span class="p">(</span><span class="n">message</span><span class="p">,</span> <span class="n">addr</span><span class="p">))</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Send </span><span class="si">%r</span><span class="s1"> to </span><span class="si">%s</span><span class="s1">&#39;</span> <span class="o">%</span> <span class="p">(</span><span class="n">message</span><span class="p">,</span> <span class="n">addr</span><span class="p">))</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span><span class="o">.</span><span class="n">sendto</span><span class="p">(</span><span class="n">data</span><span class="p">,</span> <span class="n">addr</span><span class="p">)</span>


<span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
    <span class="nb">print</span><span class="p">(</span><span class="s2">&quot;Starting UDP server&quot;</span><span class="p">)</span>

    <span class="c1"># Get a reference to the event loop as we plan to use</span>
    <span class="c1"># low-level APIs.</span>
    <span class="n">loop</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">get_running_loop</span><span class="p">()</span>

    <span class="c1"># One protocol instance will be created to serve all</span>
    <span class="c1"># client requests.</span>
    <span class="n">transport</span><span class="p">,</span> <span class="n">protocol</span> <span class="o">=</span> <span class="k">await</span> <span class="n">loop</span><span class="o">.</span><span class="n">create_datagram_endpoint</span><span class="p">(</span>
        <span class="k">lambda</span><span class="p">:</span> <span class="n">EchoServerProtocol</span><span class="p">(),</span>
        <span class="n">local_addr</span><span class="o">=</span><span class="p">(</span><span class="s1">&#39;127.0.0.1&#39;</span><span class="p">,</span> <span class="mi">9999</span><span class="p">))</span>

    <span class="k">try</span><span class="p">:</span>
        <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">3600</span><span class="p">)</span>  <span class="c1"># Serve for 1 hour.</span>
    <span class="k">finally</span><span class="p">:</span>
        <span class="n">transport</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>


<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>
</pre></div>
</div>
</div>
<div class="section" id="udp-echo-client">
<span id="asyncio-udp-echo-client-protocol"></span><h3>UDP Echo Client<a class="headerlink" href="#udp-echo-client" title="Permalink to this headline">¶</a></h3>
<p>A UDP echo client, using the <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_datagram_endpoint" title="asyncio.loop.create_datagram_endpoint"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_datagram_endpoint()</span></code></a>
method, sends data and closes the transport when it receives the answer:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>


<span class="k">class</span> <span class="nc">EchoClientProtocol</span><span class="p">:</span>
    <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">message</span><span class="p">,</span> <span class="n">loop</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">message</span> <span class="o">=</span> <span class="n">message</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">loop</span> <span class="o">=</span> <span class="n">loop</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span> <span class="o">=</span> <span class="kc">None</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">on_con_lost</span> <span class="o">=</span> <span class="n">loop</span><span class="o">.</span><span class="n">create_future</span><span class="p">()</span>

    <span class="k">def</span> <span class="nf">connection_made</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">transport</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span> <span class="o">=</span> <span class="n">transport</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Send:&#39;</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">message</span><span class="p">)</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span><span class="o">.</span><span class="n">sendto</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">message</span><span class="o">.</span><span class="n">encode</span><span class="p">())</span>

    <span class="k">def</span> <span class="nf">datagram_received</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">data</span><span class="p">,</span> <span class="n">addr</span><span class="p">):</span>
        <span class="nb">print</span><span class="p">(</span><span class="s2">&quot;Received:&quot;</span><span class="p">,</span> <span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">())</span>

        <span class="nb">print</span><span class="p">(</span><span class="s2">&quot;Close the socket&quot;</span><span class="p">)</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>

    <span class="k">def</span> <span class="nf">error_received</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">exc</span><span class="p">):</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;Error received:&#39;</span><span class="p">,</span> <span class="n">exc</span><span class="p">)</span>

    <span class="k">def</span> <span class="nf">connection_lost</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">exc</span><span class="p">):</span>
        <span class="nb">print</span><span class="p">(</span><span class="s2">&quot;Connection closed&quot;</span><span class="p">)</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">on_con_lost</span><span class="o">.</span><span class="n">set_result</span><span class="p">(</span><span class="kc">True</span><span class="p">)</span>


<span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
    <span class="c1"># Get a reference to the event loop as we plan to use</span>
    <span class="c1"># low-level APIs.</span>
    <span class="n">loop</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">get_running_loop</span><span class="p">()</span>

    <span class="n">message</span> <span class="o">=</span> <span class="s2">&quot;Hello World!&quot;</span>
    <span class="n">transport</span><span class="p">,</span> <span class="n">protocol</span> <span class="o">=</span> <span class="k">await</span> <span class="n">loop</span><span class="o">.</span><span class="n">create_datagram_endpoint</span><span class="p">(</span>
        <span class="k">lambda</span><span class="p">:</span> <span class="n">EchoClientProtocol</span><span class="p">(</span><span class="n">message</span><span class="p">,</span> <span class="n">loop</span><span class="p">),</span>
        <span class="n">remote_addr</span><span class="o">=</span><span class="p">(</span><span class="s1">&#39;127.0.0.1&#39;</span><span class="p">,</span> <span class="mi">9999</span><span class="p">))</span>

    <span class="k">try</span><span class="p">:</span>
        <span class="k">await</span> <span class="n">protocol</span><span class="o">.</span><span class="n">on_con_lost</span>
    <span class="k">finally</span><span class="p">:</span>
        <span class="n">transport</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>


<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>
</pre></div>
</div>
</div>
<div class="section" id="connecting-existing-sockets">
<span id="asyncio-example-create-connection"></span><h3>Connecting Existing Sockets<a class="headerlink" href="#connecting-existing-sockets" title="Permalink to this headline">¶</a></h3>
<p>Wait until a socket receives data using the
<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_connection" title="asyncio.loop.create_connection"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_connection()</span></code></a> method with a protocol:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>
<span class="kn">import</span> <span class="nn">socket</span>


<span class="k">class</span> <span class="nc">MyProtocol</span><span class="p">(</span><span class="n">asyncio</span><span class="o">.</span><span class="n">Protocol</span><span class="p">):</span>

    <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">loop</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span> <span class="o">=</span> <span class="kc">None</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">on_con_lost</span> <span class="o">=</span> <span class="n">loop</span><span class="o">.</span><span class="n">create_future</span><span class="p">()</span>

    <span class="k">def</span> <span class="nf">connection_made</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">transport</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span> <span class="o">=</span> <span class="n">transport</span>

    <span class="k">def</span> <span class="nf">data_received</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">data</span><span class="p">):</span>
        <span class="nb">print</span><span class="p">(</span><span class="s2">&quot;Received:&quot;</span><span class="p">,</span> <span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">())</span>

        <span class="c1"># We are done: close the transport;</span>
        <span class="c1"># connection_lost() will be called automatically.</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">transport</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>

    <span class="k">def</span> <span class="nf">connection_lost</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">exc</span><span class="p">):</span>
        <span class="c1"># The socket has been closed</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">on_con_lost</span><span class="o">.</span><span class="n">set_result</span><span class="p">(</span><span class="kc">True</span><span class="p">)</span>


<span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
    <span class="c1"># Get a reference to the event loop as we plan to use</span>
    <span class="c1"># low-level APIs.</span>
    <span class="n">loop</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">get_running_loop</span><span class="p">()</span>

    <span class="c1"># Create a pair of connected sockets</span>
    <span class="n">rsock</span><span class="p">,</span> <span class="n">wsock</span> <span class="o">=</span> <span class="n">socket</span><span class="o">.</span><span class="n">socketpair</span><span class="p">()</span>

    <span class="c1"># Register the socket to wait for data.</span>
    <span class="n">transport</span><span class="p">,</span> <span class="n">protocol</span> <span class="o">=</span> <span class="k">await</span> <span class="n">loop</span><span class="o">.</span><span class="n">create_connection</span><span class="p">(</span>
        <span class="k">lambda</span><span class="p">:</span> <span class="n">MyProtocol</span><span class="p">(</span><span class="n">loop</span><span class="p">),</span> <span class="n">sock</span><span class="o">=</span><span class="n">rsock</span><span class="p">)</span>

    <span class="c1"># Simulate the reception of data from the network.</span>
    <span class="n">loop</span><span class="o">.</span><span class="n">call_soon</span><span class="p">(</span><span class="n">wsock</span><span class="o">.</span><span class="n">send</span><span class="p">,</span> <span class="s1">&#39;abc&#39;</span><span class="o">.</span><span class="n">encode</span><span class="p">())</span>

    <span class="k">try</span><span class="p">:</span>
        <span class="k">await</span> <span class="n">protocol</span><span class="o">.</span><span class="n">on_con_lost</span>
    <span class="k">finally</span><span class="p">:</span>
        <span class="n">transport</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
        <span class="n">wsock</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>

<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>
</pre></div>
</div>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p>The <a class="reference internal" href="asyncio-eventloop.html#asyncio-example-watch-fd"><span class="std std-ref">watch a file descriptor for read events</span></a> example uses the low-level
<a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.add_reader" title="asyncio.loop.add_reader"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.add_reader()</span></code></a> method to register an FD.</p>
<p class="last">The <a class="reference internal" href="asyncio-stream.html#asyncio-example-create-connection-streams"><span class="std std-ref">register an open socket to wait for data using streams</span></a> example uses high-level streams
created by the <a class="reference internal" href="asyncio-stream.html#asyncio.open_connection" title="asyncio.open_connection"><code class="xref py py-func docutils literal notranslate"><span class="pre">open_connection()</span></code></a> function in a coroutine.</p>
</div>
</div>
<div class="section" id="loop-subprocess-exec-and-subprocessprotocol">
<span id="asyncio-example-subprocess-proto"></span><h3>loop.subprocess_exec() and SubprocessProtocol<a class="headerlink" href="#loop-subprocess-exec-and-subprocessprotocol" title="Permalink to this headline">¶</a></h3>
<p>An example of a subprocess protocol used to get the output of a
subprocess and to wait for the subprocess exit.</p>
<p>The subprocess is created by th <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.subprocess_exec" title="asyncio.loop.subprocess_exec"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.subprocess_exec()</span></code></a> method:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>
<span class="kn">import</span> <span class="nn">sys</span>

<span class="k">class</span> <span class="nc">DateProtocol</span><span class="p">(</span><span class="n">asyncio</span><span class="o">.</span><span class="n">SubprocessProtocol</span><span class="p">):</span>
    <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">exit_future</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">exit_future</span> <span class="o">=</span> <span class="n">exit_future</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">output</span> <span class="o">=</span> <span class="nb">bytearray</span><span class="p">()</span>

    <span class="k">def</span> <span class="nf">pipe_data_received</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">fd</span><span class="p">,</span> <span class="n">data</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">output</span><span class="o">.</span><span class="n">extend</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>

    <span class="k">def</span> <span class="nf">process_exited</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">exit_future</span><span class="o">.</span><span class="n">set_result</span><span class="p">(</span><span class="kc">True</span><span class="p">)</span>

<span class="k">async</span> <span class="k">def</span> <span class="nf">get_date</span><span class="p">():</span>
    <span class="c1"># Get a reference to the event loop as we plan to use</span>
    <span class="c1"># low-level APIs.</span>
    <span class="n">loop</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">get_running_loop</span><span class="p">()</span>

    <span class="n">code</span> <span class="o">=</span> <span class="s1">&#39;import datetime; print(datetime.datetime.now())&#39;</span>
    <span class="n">exit_future</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">Future</span><span class="p">(</span><span class="n">loop</span><span class="o">=</span><span class="n">loop</span><span class="p">)</span>

    <span class="c1"># Create the subprocess controlled by DateProtocol;</span>
    <span class="c1"># redirect the standard output into a pipe.</span>
    <span class="n">transport</span><span class="p">,</span> <span class="n">protocol</span> <span class="o">=</span> <span class="k">await</span> <span class="n">loop</span><span class="o">.</span><span class="n">subprocess_exec</span><span class="p">(</span>
        <span class="k">lambda</span><span class="p">:</span> <span class="n">DateProtocol</span><span class="p">(</span><span class="n">exit_future</span><span class="p">),</span>
        <span class="n">sys</span><span class="o">.</span><span class="n">executable</span><span class="p">,</span> <span class="s1">&#39;-c&#39;</span><span class="p">,</span> <span class="n">code</span><span class="p">,</span>
        <span class="n">stdin</span><span class="o">=</span><span class="kc">None</span><span class="p">,</span> <span class="n">stderr</span><span class="o">=</span><span class="kc">None</span><span class="p">)</span>

    <span class="c1"># Wait for the subprocess exit using the process_exited()</span>
    <span class="c1"># method of the protocol.</span>
    <span class="k">await</span> <span class="n">exit_future</span>

    <span class="c1"># Close the stdout pipe.</span>
    <span class="n">transport</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>

    <span class="c1"># Read the output which was collected by the</span>
    <span class="c1"># pipe_data_received() method of the protocol.</span>
    <span class="n">data</span> <span class="o">=</span> <span class="nb">bytes</span><span class="p">(</span><span class="n">protocol</span><span class="o">.</span><span class="n">output</span><span class="p">)</span>
    <span class="k">return</span> <span class="n">data</span><span class="o">.</span><span class="n">decode</span><span class="p">(</span><span class="s1">&#39;ascii&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">rstrip</span><span class="p">()</span>

<span class="k">if</span> <span class="n">sys</span><span class="o">.</span><span class="n">platform</span> <span class="o">==</span> <span class="s2">&quot;win32&quot;</span><span class="p">:</span>
    <span class="n">asyncio</span><span class="o">.</span><span class="n">set_event_loop_policy</span><span class="p">(</span>
        <span class="n">asyncio</span><span class="o">.</span><span class="n">WindowsProactorEventLoopPolicy</span><span class="p">())</span>

<span class="n">date</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">get_date</span><span class="p">())</span>
<span class="nb">print</span><span class="p">(</span><span class="n">f</span><span class="s2">&quot;Current date: </span><span class="si">{date}</span><span class="s2">&quot;</span><span class="p">)</span>
</pre></div>
</div>
<p>See also the <a class="reference internal" href="asyncio-subprocess.html#asyncio-example-create-subprocess-exec"><span class="std std-ref">same example</span></a>
written using high-level APIs.</p>
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  <ul>
<li><a class="reference internal" href="#">Transports and Protocols</a><ul>
<li><a class="reference internal" href="#transports">Transports</a><ul>
<li><a class="reference internal" href="#transports-hierarchy">Transports Hierarchy</a></li>
<li><a class="reference internal" href="#base-transport">Base Transport</a></li>
<li><a class="reference internal" href="#read-only-transports">Read-only Transports</a></li>
<li><a class="reference internal" href="#write-only-transports">Write-only Transports</a></li>
<li><a class="reference internal" href="#datagram-transports">Datagram Transports</a></li>
<li><a class="reference internal" href="#subprocess-transports">Subprocess Transports</a></li>
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<li><a class="reference internal" href="#protocols">Protocols</a><ul>
<li><a class="reference internal" href="#base-protocols">Base Protocols</a></li>
<li><a class="reference internal" href="#base-protocol">Base Protocol</a></li>
<li><a class="reference internal" href="#streaming-protocols">Streaming Protocols</a></li>
<li><a class="reference internal" href="#buffered-streaming-protocols">Buffered Streaming Protocols</a></li>
<li><a class="reference internal" href="#datagram-protocols">Datagram Protocols</a></li>
<li><a class="reference internal" href="#subprocess-protocols">Subprocess Protocols</a></li>
</ul>
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<li><a class="reference internal" href="#examples">Examples</a><ul>
<li><a class="reference internal" href="#tcp-echo-server">TCP Echo Server</a></li>
<li><a class="reference internal" href="#tcp-echo-client">TCP Echo Client</a></li>
<li><a class="reference internal" href="#udp-echo-server">UDP Echo Server</a></li>
<li><a class="reference internal" href="#udp-echo-client">UDP Echo Client</a></li>
<li><a class="reference internal" href="#connecting-existing-sockets">Connecting Existing Sockets</a></li>
<li><a class="reference internal" href="#loop-subprocess-exec-and-subprocessprotocol">loop.subprocess_exec() and SubprocessProtocol</a></li>
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